The use of hot melt gaskets and seals in container closures has gained wide acceptance in the past several years. These hot melts traditionally have been based upon either an ethylene vinyl acetate copolymer and/or a styrenic block copolymer.
While generally acceptable, these hot melt gaskets suffer from cracking or cut-through when the closure is applied to the container. Cracking appears as a series of small cracks in the surface of the gasket. These cracks may extend through a portion or the entirety of the gasket resulting in leakage. Cut-through is exhibited as an actual cut in a part or whole of the gasket. This too causes leakage problems. Additionally, it can cause a portion of the gasket to fall out of the closure upon removal from the container, making a complete seal impossible on reapplication of the closure to the container. The problems of cracking and cut-through are especially serious in containers which have thin flexible closures, which are subjected to excessive headloads, and/or which are subjected to elevated temperatures.
Most of these problems are encountered during the filling or processing of products such as during pasteurization or during warehouse storage where containers are stacked upon each other and subjected to long periods of elevated temperatures.
The present invention provides a solution to the problem of cracking and cut-through in hot melt gaskets.